Bob Butler set up a memorial at the Central Christian Church for those injured and killed in the Fort Hood shootings near Killeen. Tributes could be seen around town, and flags were flying at half-staff.

FORT HOOD — Federal and military officials have interviewed more than 170 witnesses as part of an intensive search for answers into the deadliest massacre on a U.S. military installation.

Law enforcement officers seized computers and e-mails belonging to Army Maj. Nidal Malik Hasan in an attempt to piece together what might have motivated the Army psychiatrist to allegedly open fire on the post, killing 13 and injuring 29.

Hasan, 39, was in stable condition at Brooke Army Medical Center, where he was taken off a ventilator late Saturday. Hospital officials reported he was conscious and talking, although none of his statements was made public.

Seventeen of his victims remained hospitalized.

“There is a possibility that some of these patients have been physically impaired for the rest of their lives, and there is certainly no doubt that many of them will be psychologically impaired for the rest of their lives,” said W. Roy Smythe, chief of surgery for Scott & White Hospital in Temple.

Sgt. Kimberly Munley, the civilian officer praised as a hero for exchanging gunfire with Hasan, was reportedly doing well after undergoing a second surgery Saturday. She was shot in one wrist and in her left leg and knee.

Gov. Rick Perry met with some of the injured, praising GIs and police who “raced towards the sound of the gunfire” as the rampage began.

“What I heard time after time in those hospital rooms was that it's their honor to be able to serve our country, and that is a very humbling thing to watch a young man or woman whose life has been irreparably harmed in a violent act, yet their concern and their interest is in continuing to be able to serve this country,” Perry said in a written statement.

A post on guard

Back on the post, Fort Hood assumed the appearance of an armed camp. A soldier with an M-4 rifle stood guard outside the visitor center, where a large international media contingent has assembled. Others stood sentinel at other sensitive locations on the post.

FBI agents and Army investigators continued to comb the grounds of Fort Hood's Soldier Readiness Center. Soldiers kept visitors from strolling near the knoll where investigators believe the gunman fired into hundreds of unarmed soldiers.

The Army said no motive for the shooting had yet been established. Others surmised that the Virginia native, who counseled soldiers with post-traumatic stress disorder, might have internalized his patients' issues. Those who know him have said Hasan was opposed to the wars and was stressed about being stationed overseas.

Sergeant's story

One of two police officers who confronted the suspect says he shot Hasan before kicking the man's weapon away, handcuffing him and ending the nation's worst killing spree on a military base.

Sgt. Mark Todd joined Munley in a firefight with Hasan that lasted less than a minute. Todd, 42, was not wounded, but the exchange left Munley injured and Hasan critically wounded.

Seconds after Todd arrived on the scene, he said, he saw a calm-looking Hasan, his gun drawn and his fingers pointing at people.

“He was firing at people as they were trying to run and hide,” Todd told The Associated Press on Saturday.

That's when Todd, a retired soldier who now works as a civilian police officer at Fort Hood, said he shouted at Hasan. “I told him, ‘Stop, and drop your weapons.' I identified myself as police, and he turned and fired a couple of rounds at me. I didn't hear him say a word. ... He just turned and fired.”

There has been confusion since Thursday's rampage about whose bullets actually brought down Hasan, who was shot four times. At first, Munley's supervisor said it was her shot to Hasan's torso , but Army officials would say only that an investigation was under way.

Authorities recovered two handguns believed to have been carried by Hasan during the assault, a 5.7mm pistol and a .357 magnum. Both were sent to a federal crime lab in Atlanta. A Fort Hood official said it appears that only one weapon was fired.

Obama to visit

President Barack Obama will attend a memorial service Tuesday honoring the victims. He praised those who ended the shootings and lauded the armed services' diversity — a move designed to calm tensions about Hasan.

“They are Americans of every race, faith and station. They are Christians and Muslims, Jews and Hindus and nonbelievers,” Obama said in his radio and Internet address Saturday.

The Department of Veterans Affairs sent four Mobile Vet Centers to the Fort Hood area to bolster counseling services. As Sunday services neared, Col. Frank Jackson said his talk at the 73rd Street Chapel would be about communities of faith and how hope, encouragement and healing can help overcome the tragedy.

“This is a painful time,” said Jackson, a 58-year-old Southern Baptist who acts as the post's garrison chaplain. “It's painful, but it's powerful.”

Some veteran soldiers of the Iraq war said they were not surprised by the tragedy.

“In a way, it was like it's waiting to happen,” Spc. Travis McRae said. “The Army has an awesome way of getting you ready for war. It gets you in that mind-set to go over there and fight, but whenever you come back, they don't have a way of turning that switch off.”